It happened at 71st Street and Binforld Boulevard just after 3 p.m.
Officials say 18 North Central High School students were on the Washington Township bus when it collided with an SUV.
Three students were taken to the hospital after suffering minor injuries. The bus driver was also taken to the hospital to be checked out.
The SUV driver, an unidentified woman, had to be extricated from her vehicle. She was taken to the hospital in critical condition.
Officials said the SUV driver pulled out in front of the bus.
The crash remains under investigation.